As a toner fixing unit used in an image forming apparatus, a toner fixing unit of a type in which a toner image corresponding to image information is carried and formed on a recording sheet through an operation process of an electrophotographic system, and unfixed toner is then heated and fixed while the recording sheet is moved, is commonly used.
The fixing unit sandwiches, by fixing means and pressurizing means, the recording sheet and the toner carried on the recording sheet by static electricity, moves the recording sheet and the toner while applying heat and pressure to the recording sheet and the toner, thereby melting and fixing the toner to the recording sheet. The fixing means includes a roller that conveys the recording sheet and the toner while rotating, and the pressurizing means includes a roller that rotates in a direction opposite to a direction of the roller of the fixing means while being in pressure contact with the fixing means.
Temperature of each of the rollers largely influences image quality. Therefore, the temperature of a surface of each of the rollers is detected by a sensor and is controlled.
An infrared temperature sensor that detects temperature of a roller of a fixing unit in a non-contact manner in order to avoid damage of the roller, is well-known (for example, Patent Literatures 1, 2, and 3). The infrared temperature sensor includes an infrared detection element and a temperature compensation element on a heat conversion film, detects, by the infrared detection element, an infrared radiation heat quantity of the roller that is fixing means as a detection object, further detects atmospheric temperature by the temperature compensation element to compensate the temperature, thereby specifying the temperature of the detection object.